Occlusive diseases of the vasculature are a leading cause of mortality and morbidity. While the nature of vascular diseases vary greatly, the underlying clinical cause is basically a reduction in blood flow due to an accumulation of obstructive material in the vessels feeding (arteries) or draining (veins) the affected organ. The obstructive material varies in hardness and composition. Harder obstructive material often contain calcified atherosclerotic plaque whereas softer material often contains blood clots (thrombus) and the disease is commonly caused by a combination of the two.
When such obstructions develop abruptly in the coronary vessels (feeding the heart), a heart attack occurs and in the brain it is referred to as a stroke. When obstructions develop over a longer period in the coronary vessels patients experience angina; while in the legs, they may suffer from pain ulcers and gangrene.
Clinical treatment of a vascular disease may involve surgical, pharmaceutical, or catheter based therapies. The choice of treatment depends on many factors, including the extent and location of disease and the nature of the obstruction. Surgical methods for treating vascular occlusive disease tend to be highly invasive and are typically associated with longer hospital stays and higher costs. Pharmaceutical treatment with thrombus dissolving drugs takes time to work, may inadvertently cause bleeding elsewhere in the body and may also dislodge large particles of obstructive material which is undesirable. Catheter-based therapies use various mechanisms to fragment, displace or remove vascular obstructions, and when such catheters are used percutaneously they offer shortened procedure times and reduced hospital stays.
Various designs of catheters have been developed for removing harder obstructive material from the vasculature.
For example, U.S. Pat. No. 4,669,469 (Gifford) shows a catheter with a distal cylindrical housing with a side window that excises the obstructive material with a rotating blade disposed in the housing. However, the rigidity of the housing limits the utility of the device in tortuous vessels such as coronary arteries so that in the process of advancing such a rigid device past the material to bring the side window into position, it may dislodge some of the obstructive material down stream.
Another example is U.S. Pat. No. 4,990,134 (Auth) which shows an abrading device carried at the distal end of a flexible drive shaft. The device uses a high speed abrasive burr that pulverizes hard atherosclerotic but is less effective in dealing with soft tissue like material which may be dislodged into the blood and travel downstream.
Other designs of catheters have been developed for removing softer obstructive material from the vasculature.
For example, U.S. Pat. No. 6,287,271 (Dubrul) shows a combination of rotational and longitudinal vibrations together with an injection of a lysing agent to break up the obstructive material in the vessels with an optional aspiration channel that is located proximally at a distance from the area where the tip fragments the material. Thus, once the obstructive material is fragmented some of the fragments may flow with the blood downstream.
Another example is U.S. Pat. No. 5,476,450 (Ruggio) and U.S. Pat. No. 5,938,645 (Gordon) that show an asymmetrically partitioned lumen whose cross-sectional moment of inertia is higher in certain direction. This asymmetry together with the off-center position of the guidewire, makes it harder for the catheter to turn while advancing along a three dimensional path that is commonly encountered in the vasculature of the heart and elsewhere.
The present invention generally relates to medical devices and, more particularly, to a catheter for removing soft obstructive material such as thrombus from a patient""s vasculature.
In accordance with one aspect of the present invention, a flexible catheter is provided having a guidewire lumen extending throughout its length and a distal section that is insertable, over a guidewire, into a patient""s vasculature for removing an obstructive material. The catheter comprises a guidewire shield in the form of an inner tube nested in an outer tube with an unobstructed void defined between them that is connectable to negative pressure.
The inner tube is preferably rotated by a motor to reduce the frictional resistance to the sliding of the inner tube over the guidewire as well as for reducing the frictional resistance to the movement of obstructive material through the void. The direction of the rotation of the inner tube is reversible to avoid wrapping-up blood fibers around the inner tube, thus avoiding the creation of a new very resilient obstruction on the inner tube. Additionally, the inner tube may have a non-circular cross section to agitate the obstructive material that is passing through the void and prevent the material from organizing to form an obstruction therein. To enhance the flexibility of the distal portion of the catheter a wall thickness of the inner tube can be reduced, gradually or in steps, since the torque that the inner tube has to carry lessens towards the distal end.
The distal section of the catheter consists essentially of the distal portions of the tubes which are made preferably from an flexible biocompatible plastic material minimizing the mechanical trauma to the vasculature. The inner tube has no connection to any element for cutting or fragmenting the obstructive material so as not to disturb the obstructive material while it is still in the vasculature, prior to being aspirated into the void, thereby reducing the danger of releasing material fragments into the blood stream. Thus, the only effect of the rotation of the inner tube on the material is to minimize the resistance to movement of the material that already has been aspirated into the void in response to the negative pressure that prevails in the void.
In accordance with another aspect of the present invention, a method of removing obstructive material from a vasculature is provided, comprising several steps:
Introducing a guidewire, through a patient""s vasculature to the vicinity of the obstructive material.
Inserting into the vasculature, over the guidewire, a distal section of a catheter, with an inner tube nested in an outer tube, to the vicinity of the obstructive material while selectively rotating the inner tube as needed to reduce the frictional resistance to movement of the catheter over the guidewire.
Creating negative pressure in a void that is defined between the tubes.
Selectively rotating the inner tube as needed to reduce the frictional resistance to movement of the material and to optionally agitate the material that is already in the void.
Withdrawing the catheter from the patient.